::s1:: do   
    local c = io.read(1)
    if c == '0' then
        goto s2
    elseif c == nil then print "ok";return
    else goto s1
    end
end
::s2:: do
    local c = io.read(1)
    if c == '0' then
        goto s1
    elseif c == nil then print "not ok";return
    else goto s2
    end
end
goto s1